# motion and forces

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• Created by: ikayleigh
• Created on: 05-06-16 15:27
• motion and forces
• stopping    distance    increase    -increasing speed          -     a greater mass               -reduced friction          -  increased reaction time
• air resistance (in gases) and drag (in liquids), from frictional forces between the fluid and an object, increase as      -the objects speed increases         -the fluid gets denser
• an object falling through a fluid, accelerates until it reaches terminal velocity, when the resultant force is zero :upthrust (fluid resistance force) = objects weight due to gravity
• every moving object has kinetic energy that can be transformed into other forms.           An objects kinetic energy increases when its:          - mass increases         -speed increases
• using force to do work on an object gives energy               work done=energy transferred
• the amount of work done depends on the force and the distance work done (J) = force (N) x distance moved in the direction of the force (m)
• every moving object has momentum that depends ion its mass and velocity momentum (kg m/s) =mass (kg) x velocity (m/s)
• momentum has size and direction and is conserved in collision and explosions
• forces changes and objects momentum by changing its velocity or direction. the bigger the force on a moving object, the larger its rate of changing momentum
• distance-time graphs helps us to "picture" how an object moves:            -the slope on the graph shows the speed
• average speed=total distance travelled/total time travelled
• the velocity of an object tells us its speed in a given direction. acceleration is the rate of change of velocity.             acceleration (m/s squared ) =change in velocity (m/s) /time taken to change (s)
• velocity-time graphs show how the velocity changes:        -the slope shows the acceleration    -the area under the graph shows the distance travelled
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• force can add up or cancel out to give a resultant force. When the resultant force is not zero, an object accelerates. the acceleration is:                   -directly proportional to force, a&f         -inversely proportional to mass, a&1/m                resultant force (bn) =mass (KG) x acceleration (M/s squared)  F=ma
• for every force there is an equal and opposite force, balanced forces have the same value but act in opposite directions, e.g. a person floating in water has a balanced force
• objects moving at constant velocity (including terminal velocity) have balanced forces.
• stopping distance=thinking distance breaking distance             thinking distance=speed x reaction time